Topological Sort

In what kind of situation will we need to use topological sort?

Precedence(优先级) scheduling, say given a set of tasks to be completed with precedence constraints, in which order should we schedule the tasks? One simple example are classes in university, you need to take introduction to computer science before you take advanced programming, so this is the constraint, you need to do A before you do B, now I give you many tasks, and they have many constraints, in what kind of order should you do these tasks?

Where does topological sort come from?

It comes from Digraph Processing, because this kind of problem can be modeled as a DiGraph, vertex = task, edge = precedence constraint.

Limitation

Topological Sort only exists in DAG(Directed Acyclic Graph), so you need to run a DFS first to make sure that the graph is a DAG.

Algorithm

1, Run depth-first search

2, Return vertices in reverse postorder

Reverse DFS postorder of a DAG is a topological order

Code

复制代码
public class DepthFirstOrder
{
    private boolean[] marked;
    private Stack<Integer> reversePost;
    
    public DepthFirstOrder(Digraph G)
    {
        reversePost = new Stack<Integer>();
        marked = new Boolean[G.V()];
        for (int v = 0; v < G.V(); v++)
        {
            if (!marked[v])
            {
                dfs(G, v);
            }
        }
    }

    private void dfs(Digraph G, int v)
    {
        marked[v] = true;
        for (int w : G.adj(v))
        {
            if (!marked[w])
            {
                dfs(G, w);
            }
        }
        reversePost.push(v);
    }
    
    public Iterable<Integer> reversePost()
    {
        return reversePost;
    }
}
View Code
复制代码

 

posted on   dingjunnan  阅读(383)  评论(0编辑  收藏  举报

编辑推荐:
· Linux glibc自带哈希表的用例及性能测试
· 深入理解 Mybatis 分库分表执行原理
· 如何打造一个高并发系统?
· .NET Core GC压缩(compact_phase)底层原理浅谈
· 现代计算机视觉入门之:什么是图片特征编码
阅读排行:
· 手把手教你在本地部署DeepSeek R1,搭建web-ui ,建议收藏!
· Spring AI + Ollama 实现 deepseek-r1 的API服务和调用
· 数据库服务器 SQL Server 版本升级公告
· C#/.NET/.NET Core技术前沿周刊 | 第 23 期(2025年1.20-1.26)
· 程序员常用高效实用工具推荐,办公效率提升利器!

导航

< 2025年1月 >
29 30 31 1 2 3 4
5 6 7 8 9 10 11
12 13 14 15 16 17 18
19 20 21 22 23 24 25
26 27 28 29 30 31 1
2 3 4 5 6 7 8
点击右上角即可分享
微信分享提示